Sayyiduna Jabalah (may Allah be pleased with him) narrates that the Prophet (peace and blessings be upon him) said: "Whoever separates from the Jama'ah by a hand-span has separated from Islam."
This narration has been recorded by Imam al-Bazzar. Its chain contains one narrator, Muhammad bin Ubaydullah al-Arzami, and he is da'if (weak).
Hadith Referenceمجمع الزوائد ومنبع الفوائد / كتاب الخلافة / 9135